This study continues to be concerned with establishing detailed karyotypic aspects of cancer of the bladder with particular emphasis on papillary tumors. Cytogenetic criteria of help to the clinician in predicting possible recurrence of papillary tumors, such as the presence of marker chromosomes and other structural anomalies, have received and will continue to receive primary attention. A study based on the staining of rDNA of the acrocentric chromosomes and the application of this technique to the establishment of subtle translocations involving such chromosomes, is being now utilized in our laboratory. Another aspect of the study is concerned with the chromosome constitution of transitional cell cancers of the bladder and a correlation of the cytogenetic findings with the therapeutic and biologic behavior of these cancers. Emphasis is being put on the changes involving certain chromosome groups, e.g., #1 and #14, as biologic indicators of the behavior of such tumors.